Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 3 Cells

Cells are the simplest structural and functional unit of living organisms There are about 75 trillion cells in the human body Many different types of specialized cells in the human body

3.1 Cell Structure Plasma Membrane –Outer boundary of the cell –Barrier to water-soluble materials inside and outside the cell –Composition Two layers of phospholipids molecules Cholesterol

Proteins are attached to or embedded in the phospholipid layers –Passageways for transport of substances in and out of the cell –Receptors for enzymes and hormones –With carbohydrates serve as identification markers

Plasma membrane is selectively permeable –Allows only certain molecules to enter or exit the cell –What can pass through is determined by Molecular size Solubility Ionic charges Attachment to carrier molecules

Cytoplasm –Fluid or gel-like substance that fills the interior of the cell –75% to 90% water plus organic and inorganic molecules –Semitransparent, thicker than water –Supported by Intracellular membranes Cytoskeleton

Organelles –Tiny organs in the cytoplasm –Perform specific roles in the cell –Distinguished by size, shape, structure, and function

Types of Organelles Nucleus –Largest organelle –Nuclear envelope separates it from the cytoplasm Has pores that aid in movement of materials between the nucleus and cytoplasm

–Contains chromosomes made of DNA and protein 46 total chromosomes per nucleus; 23 pairs DNA contains instructions that control cell function Chromatin –Nucleoli contain RNA and protein and are site of ribosome production

Ribosomes –Composed of ribosomal RNA and protein –Site of protein synthesis in cells –Occur singly or in clusters

Endoplasmic Reticulum or ER –Membranes that extend from the nucleus throughout cytoplasm –Functions Support cytoplasm Channels to facilitate movement of materials within the cell –Two types of ER Rough ER Smooth ER

–Rough ER Has numerous, attached ribosomes Proteins made here are exported from cell

–Smooth ER Lacks ribosomes Site of lipid synthesis

Golgi Complex –Stack of flattened membranous sacs –Processes and sorts synthesized substances into vesicles Secretory vesicles

Mitochondria –Possess an inner folded membrane (cristae) and outer smooth membrane –Site of aerobic cellular respiration –“Powerhouse” of the cell

Lysosomes –Contain powerful digestive enzymes –Function to digest Bacteria entering cell Cell parts to be replaced Damaged or worn out cells

The Cytoskeleton –Microtubules Long, thin tubules Support for cell and movement of organelles –Microfilaments Tiny rods of contractile protein Support cell and enable movement

Centrioles –Two short cylinders of microtubules near nucleus and oriented at right angles –Form and organize spindle fibers during cell division –Involved in forming microtubules in cilia and flagella

Cilia –Numerous, short hair-like projections containing microtubules –Move substances along cell surface

Flagella –Long, whip-like projections containing microtubules –Enables for movement of cells –Example: sperm

Microvilli –Extensions of the plasma membrane –Increase cell surface area and aid in substance absorption into the cell –Abundant in intestinal cells

3.2 Transport Through Plasma Membranes Movement of substances through the plasma membrane occurs by one of two processes –Passive transport: movement without cell assistance –Active transport: movement requiring ATP as the cell assists in transport

Passive Transport Diffusion –Net movement of molecules from an area of higher concentration to an area of lower concentration –Occurs in gases and liquids due to constant, random motion of molecules –Occurs in both living and non-living systems

Osmosis –Diffusion of water through a selectively permeable membrane –Water moves from area of higher water concentration (lower solute concentration) to area of lower water concentration (higher solute concentration)

–Water always diffuses from a hypotonic solution into a hypertonic solution –Hypotonic solution Has a lower concentration of solutes and higher concentration of water –Hypertonic solution Has a higher concentration of solutes and lower concentration of water –Isotonic solution Solutions have the same concentration of solutes and water

Filtration –Forces smaller molecules in a solution through a membrane due to greater hydrostatic pressure on one side –Hydrostatic pressure is the pressure exerted by a fluid against a wall or membrane

Active Transport Requires the cell to use ATP Three basic mechanisms –Carrier proteins –Endocytosis –Exocytosis

Carrier Proteins –Located in the plasma membrane with the ability to bind molecule or ion –Uses energy to change shape and move the molecule/ion from one side of the membrane to the other –From area of low concentration to area of high concentration

Endocytosis and Exocytosis –Used for materials too large for carrier proteins –Endocytosis: engulfment of particles and liquid droplets Phagocytosis Pinocytosis –Exocytosis: substances are expelled from the cell

–Steps of endocytosis Plasma membrane is used to surround and internalize the substance in a vesicle

3.3 Cellular Respiration Process that breaks down nutrients to release energy and transfer some of this energy into ATP Involves two sequential processes –Anaerobic respiration –Aerobic respiration

Anaerobic Respiration –No oxygen is required –Occurs in the cytoplasm –Uses 1 glucose molecule to produce 2 pyruvic acid molecules and 2 ATP

Aerobic Respiration –Requires oxygen –Occurs in mitochondria –Changes 2 pyruvic acid molecules into carbon dioxide, water, and 36 ATP

Overall, cellular respiration yields 36 ATP from one glucose molecule

3.4 Protein Synthesis DNA and the genetic code –DNA consists of 2 strands of nucleotides held together by hydrogen bonds between organic bases –Organic bases are adenine, thymine, cytosine, guanine

–Organic bases exhibit complimentary base pairing –Sequence of bases forms the genetic code

–A gene, the unit of inheritance, is a specific sequence of bases in DNA –Genes are responsible for Directing cell functions Determining hereditary traits by controlling protein synthesis

The Role of RNA –RNA consists of a single strand of nucleotides –The organic bases are adenine, uracil, cytosine, guanine –Produced in the nucleus by using a DNA strand as a template –Involved with protein synthesis

3.5 Cell Division Two types of division occur in the body –Mitotic Cell Division Parent cell forms daughter cells with identical chromosomes to the parent –Meiotic Cell Division Parent cell forms daughter cells with only half the number of chromosomes

Mitotic Cell Division –Produces new cells for growth and for replacement of worn or damaged cells –Involves three processes Replication of chromosomes Mitosis Division of the cytoplasm

–The cell cycle is the time between cell divisions Mitosis is only 5-10% of the cell cycle Interphase is the time when mitosis is not occurring

–During interphase, there is growth and replication of chromosomes and centrioles The DNA strands “unzip” forming two strands of DNA New nucleotides join the existing strands through complimentary base pairing When completed, each new DNA molecule consists of an “old” strand joined to a “new” strand

Mitotic Phases –Mitosis can be divided into four sequential processes –Prophase Chromosomes condense and become rod- shaped Each chromosome consists of two chromatids joined at their centromeres Nuclear envelop disappears Centrioles migrate to opposite ends of the cell and form the mitotic spindle

Prophase

–Metaphase Chromosomes line up at the equator of the spindle Centromeres of each chromatid pair are attached to the spindle

–Anaphase Separation of the centromeres separates the paired chromatids Then the members of each pair migrate to opposite sides of the cell

–Telophase Spindle fibers disappear and nuclear envelops reform, establishing two new nuclei Chromosomes uncoil Cytokinesis, or division of the cytoplasm, occurs

Cell Division and Cancer Abnormal cell growth Tumors (also called, neoplasm)  Benign Encapsulated (one spot)  Malignant (spreads) Invasion Metastasis Cancer—Disease that results from a malignant tumor Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Cell Division and Cancer Cancer results from mutations that disrupt the control mechanism that regulates cell growth and division. Cancers most often begin where cells are dividing rapidly, because the more chromosomes are copied, the greater the chances of error. Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings